(Name, Address and Telephone Number of Person Authorized to Receive Notices and Communications)

February 28, 2018

(Date of Event which Requires Filing of this Statement)

If the filing person has
previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D, and is filing this schedule because of §§240.13d-1(e),240.13d-1(f) or 240.13d-1(g), check the following box. ☐

CUSIP No. 31660B101

1.

Name of
Reporting Person

Leucadia National Corporation, on behalf of itself and its
controlled subsidiaries

This Amendment No. 4 amends the Statement on Schedule 13D first filed by Leucadia National Corporation
(Leucadia) on behalf of itself and its controlled subsidiaries (the Reporting Person) with the Securities and Exchange Commission on June 19, 2017, as amended by Amendment No. 1 filed on
August 18, 2017, Amendment No. 2 filed on August 31, 2017 and Amendment No. 3 filed on September 11, 2017 relating to the Common Stock, par value $0.01 per share (the Common Stock), of Fiesta Restaurant
Group, Inc., a Delaware corporation (the Issuer). The principal executive offices of the Issuer are located at 14800 Landmark Boulevard, Suite 500, Dallas, Texas 75254. Capitalized terms used herein but not otherwise defined
herein have the meanings given to them in the Schedule 13D.

Item 3.

Source and Amount of Funds or Other Consideration.

From February 28, 2018 through March 1,
2018, the Reporting Person purchased an aggregate of 599,088 shares of Common Stock. The securities were acquired by the Reporting Person using cash from working capital in the amount of approximately $10.1 million.

Item 4.

Purpose of Transaction.

The Reporting Person purchased the Common Stock reported herein for investment
purposes. The Reporting Person intends to purchase additional shares of Common Stock from time to time, if, at such time, the terms of such investment are favorable to the Reporting Person and the Reporting Person deems the investment to be prudent.

Other than described above, the Reporting Person does not have any plans or proposals of the type referred to in Items 4(a) through (j) of Schedule
13D. The Reporting Person, however, retains the right to change its intent and to pursue any transaction contemplated in Items 4(a) through (j) of Schedule 13D and, to the extent the Reporting Persons affiliates operate as broker-dealers,
they retain the right to pursue a role as a financial advisor, underwriter or placement agent with respect to any such transaction involving the Issuer and its affiliates.

Item 5.

Interest in Securities of the Issuer.

Number of shares as to which the Reporting Person has:

Sole power to vote or to direct the vote: 3,075,383

Shared power to vote or to direct the vote: 0

Sole power to dispose or to direct the disposition of: 3,075,383

Shared power to dispose or to direct the disposition of: 0

During the past sixty days, the Reporting Person engaged in the following open market purchases of Common Stock:



On February 28, 2018, the Reporting Person purchased 422,274 shares of Common Stock at a weighted average price per share of $16.9747.



On March 1, 2018, the Reporting Person purchased 176,814 shares of Common Stock at a weighted average price per share of $16.5894.

Brian P. Friedman is the President and a director of Leucadia. Mr. Friedman has also been a director of the
Issuer since April 2011. Mr. Friedman beneficially owns an aggregate of 64,938 shares of Common Stock representing approximately 0.2% of the Issuers outstanding shares. Mr. Friedmans beneficial ownership includes 36,270 shares
of Common Stock held directly and 28,668 shares of Common Stock held indirectly through a partnership.

Except as set forth in this Item 5, no person
other than each respective record owner of the securities referred to herein is known to have the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of, such securities.

SIGNATURE

After
reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.